The prevalence of interparental conflict, discord, and violence in the American family and its profound costs to children and society are indisputable. Exposure to interparental discord and conflict is specifically associated with a wide range of child psychopathology. However, large scientific gaps exist in understanding how, why, and when children exposed to interparental difficulties develop disproportionate vulnerability to mental health problems, particularly during period of heightened vulnerability that is proposed to develop during early adolescence. By situating the emotional security theory (EST) within a developmental psychopathology framework, this study is designed to address these gaps by elucidating the developmental mechanisms, pathways, and conditions underlying associations between interparental conflict and child maladjustment across childhood and adolescence. Our specific aims are to: (1) test a family-wide model of EST for early adolescence in which interparental conflict and accompanying parenting processes increase children's vulnerability to mental health problems by undermining their sense of security in interparental and parent-child relationships, (2) determine whether developmental timing and course of experiences, including child and adolescent developmental histories, alter or modify associations between family conflict, emotional security, and adolescent outcomes, (3) chart the sequence of biological, neuropsychological, and developmental processes that account for the heightened insecurity and mental health problems experienced by adolescents from high conflict homes, and (4) identify how family risk and protective factors may alter paths between interparental discord and child coping and maladjustment. This project will follow a sample of over 200 mothers, fathers, and 13-year-old children who previously participated in three waves of data collection during the early elementary school years into adolescence through the collection of three additional waves, each spaced one year apart. Utilizing a multi-method measurement battery, this prospective design will capture multiple levels of adolescent vulnerability (e.g., neuroendocrine, neuropsychological, stage-salient adaptation, psychopathology) and family adversity. Our long-term objective is to translate the scientific knowledge gained from this project into clinical treatment and social policy initiatives that are designed improve the welfare of vulnerable children and families.